Comparison of Drug Related Problems Associated with Use of Narrow Therapeutic Index Drugs and Other Drugs in Hospitalized Patients

Objectives: To identify and categorize types of Drug Related Problems (DRPs), assess various risk factors for developing DRPs and delineate if drugs with narrow therapeutic index or non-narrow therapeutic index drugs cause greater number of DRPs. Methods: Patients from General Medicine, Surgery, Psychiatry, Cardiac and Intensive Care Unit (ICU) departments of a tertiary care teaching hospital were included. Data was collected prospectively over eight months from medical history, medication charts, case notes and laboratory data. Only those patients prescribed at least five drugs were included. Pediatric and Oncology patients and pregnant women were excluded from the study. Narrow therapeutic index (NTI) drugs (Insulin, digoxin, warfarin, levothyroxine, aminoglycoside antibiotics, carbamazepine, lithium and phenytoin) were compared with non NTI-drugs to delineate patterns of DRPs between both groups. Results: A total of 200 patients were enrolled in the study, and 172 DRPs were identified. The most common DRPs were: drug interactions (63%), inappropriate drug use (10.5%) and adverse drug reactions (10.5%). Polypharmacy and duration of hospitalization were established as significant risk factors for developing DRPs. NTI-drugs had a greater risk of developing DRPs (0.22) versus non-NTI drugs (0.08). Two categories of DRPs were found to be more significantly associated with NTI-drugs: ADRs and inappropriate drug use. Conclusion: While ADR and inappropriate drug use were more common with NTI-drugs, in clinical practice other non NTI-drugs: Anti-psychotic drugs (quetiapine, amisulpride etc.) and NSAIDs (aspirin) showed a high tendency for interactions and needed frequent monitoring.